In the lawsuit ... obtained by TMZ ... Kim's lawyer, Eric George, trashes Chad Hurley, the guy who co-founded YouTube and sold it to Google for $1.65 billion. Kim claims Hurley is the one who schemed to post the video on his new Internet venture, MixBit.

Kim goes for the jugular, saying Hurley was desperate to find a "second act," after 2 flops following his YouTube sale. In the lawsuit, Kim claims Hurley wasn't even invited to AT&T Park in San Fran but manipulated his way in.

According to TMZ, Kim says they let him stay, but only after he signed a confidentiality agreement. And get this ... they even got him to take a pic holding the signed confidentiality agreement, which is attached to the lawsuit.

The couple says, "Hurley proceeded to try to turn the event into one starring himself, broadcasting the images he knew were the exclusive property rights of someone else."

Specifically, Kim and Kanye say he posted Kanye's engagement proposal on MixBit and tweeted it to nearly a million followers. He then had the audacity to issue a press release, touting his video trophy.

Kim and Kanye are suing for unspecified damages ... including punitives. Even though Kim and Kanye don't say how much the video was worth, they mention it was destined for MC Cable Television, which is an arm of Bunim/Murray and E!, which produces and broadcasts "Keeping Up with the Kardashians."